This invention relates to the rejection or detection of noise in a capacitive sensing circuit and reduction of sense plate capacitance or parasitic capacitance.
A capacitive sensing circuit used to detect touch or proximity events is easily adversely affected by noise. This problem is normally addressed by trying to adjust a de-bouncing circuit and filtering and voltage trip levels.
Appliances such as electric drills and mobile phones generate noise which is difficult to combat. The effect of noise on apparatus such as an oven, a cooking plate, a chain saw or the like, which is designed to be controlled by the use of capacitive sensing switches, responsive to touch or proximity, is unacceptable. The false detection of a touch or proximity event could have serious adverse consequences and this, in itself, limits or prevents the adoption of capacitive sensing arrangements in many applications.
Most people are aware from personal experience when talking on a landline phone that immediately before a signal comes from a mobile phone, specifically GSM, or prior to receiving a call, higher than normal energy fields are radiated by the phone which interfere with the signal on the landline phone. This leads to the conclusion that a product which may work satisfactorily under certain conditions can be adversely affected at other times.